The present invention relates to an illumination apparatus for an optical instrument and, more particularly, to an illumination apparatus for an optical microscope.
An illumination apparatus for an optical microscope has conventionally been known as one of illumination apparatuses for optical instruments with an illumination system having a lens such as a glass lens or a hard plastic lens (polycarbonate or acrylic lens).
In a lens made of an optical glass, its transmittance generally abruptly decreases from a wavelength of about 330 nm, and the lens hardly transmits light with a wavelength in the ultraviolet range. For this reason, when an ultraviolet light source is required to observe a sample or the like with a fluorescent or ultraviolet microscope, a lens made of a special material such as quartz or fluorite has conventionally been used.
The ultraviolet transmission wavelength range of the lens made of quartz or fluorite is however limited to 200 to 300 nm. Further, a special material such as quartz is very expensive and must be polished, resulting in high lens cost. Such a lens is therefore difficult to use in a low-cost optical microscope.
Some optical microscopes employ plastic lenses which can be manufactured at lower costs. However, the transmission wavelength of the plastic lens is limited similarly to the glass lens.
In the plastic lens, the heat deformation temperature of the material used is about 100.degree. C. Accordingly, if the plastic lens is used near the light source lamp, optical characteristics may degrade due to heat deformation.
In fixing an optical element inside the microscope, the lens made of an optical glass is generally adhered to a frame directly, or fitted in the frame and then pressed by a press ring.
Adhering the optical element to the frame requires an adhesive, and a long time is necessary to completely fix the optical element. In addition, attention must be paid to the operation process and the operation environment. Even pressing the lens made of an optical glass with the press ring requires another press ring. The press ring must be screwed or adhered to prevent looseness.